1. Field of the Invention
The present invention relates to improvements in an hydraulic control device for an automatic transmission of a vehicle.
2. Description of the Prior Art
It is well known that a shift change of an automatic transmission in an automotive vehicle is usually carried out by changing a connecting state of two clutches. For example, 2nd speed is produced by engagement of a first clutch and release of a second clutch, and 3rd speed is produced by release of the first clutch and engagement of the second clutch. When a drive position of the automatic transmission is changed from 2nd speed to 3rd speed, a shift valve in a control system is changed from a first state that a hydraulic chamber of the first clutch is communicated with a line pressure to a second state that a hydraulic chamber of the second clutch is communicated with the line pressure. Such an automatic transmission is disclosed in a full range electronic control type automatic transmission (5E-AT) Service Manual (Type RE5R01A). In this transmission, to control the increase of the torque power which is caused by directly applying a line pressure to the second clutch, a pressure control valve is installed between the shift valve and the second clutch. Accordingly, the line pressure from the shift valve is properly controlled and supplied to the second clutch.
However, difficulties have been encountered with the above conventional arrangement, in which it is necessary to use a relatively large space for the installation thereof. That is, since the shift valve has to change the connecting conditions of the first and second clutches, the shift valve needs to have at least five ports. This increases the axial length of the shift valve. Furthermore, since it is necessary to provide a pressure control valve in addition to the above-mentioned shift valve, another valve chamber for the pressure control valve is required to this arrangement.